I have a question pertaining to fine tuning mid range zoom lenses.
I have a D7100 and 4 Nikon lenses. If I were to check my lenses for AF accuracy according to how Nikon suggests it is done and find that a fine tune is necessary, it occurred to me that with a prime lens it seems quite straight forward. But with mid range zoom lenses is it done differently?

For example if I test the AF on a 18 - 140mm lens at 60mm would that give me a good indication if the lens AF is accurate or would I have to do the test a various focal lengths? And if a AF fine tune is required should I use the middle of the zoom range?

In case of a zoom lens I would open the zoom and get the lens as close as possible so I get DOF as shallow as possible, I think its enough to adjust it once.
I also would like to add dont try to fix lens that aint broken, if you have no issues with your lenses then why look for something that aint there ?
I used to fine tune my lenses when I had the D7000 but the problem was with the camera and nothing really solved my problems completly, when I got my D7100 all AF issues were resulved, I never needed to fine tune any of my lenses again.

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A few things to keep in mind when determining if an AF fine tune is necessary:

Keep in mind that when a lens is set to a short focal length, the autofocus bracket can cover a fairly large area; the AF brackets in the viewfinder are not always 100 percent accurate and identical to the actual area the AF system uses; this is something that's often overlooked. Very careful tests of AF systems will usually show that the brackets are a good guideline, but the actual sensitive area is smaller than the total bracketed area, so it's really important to realize, at say 18mm at 10 feet, you MIGHT very easily be aiming 2 to 3 inches off of the ACTUAL area the focus sensor reacts to! At longer distances, it can sometimes be easy to get a missed focus when the lens is in the short focal length region, due to the fact that the ACTUAL sensor area is fairly wide as distance increases, and if there's a slight say leftward bias, the AF bracket might NOT be on "the target", but rather off to the left 6 inches, and thus wayyyyyyyy behind the desired area.

Try some focusing tests using 2- or 3-inch diameter poles, like those on an outdoor clothesline, or skinny fence posts, or slender sapling trees, and see if you can determine if the AF area is actually off to the left or the right of the bracketed area, and at what range it becomes an issue.

I have found that focusing accuracy and repeatability is worse at the wider end of a zoom, and better, and more predictable at the longer end of a zoom. At the short end, depth of field is a lot less critical most of the time than it is at say, 200mm.

If a lens repeatedly mis-focuses, and you're sure the issue is not in operator error, definitely look into AF fine tuning.